This application claims the priority of Korean Patent Application No. 2003-28038, filed on May 1, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a reference picture used to encode or decode moving picture data, and more particularly, a method of determining a reference picture for blocks constituting a current picture, a method of compensating for a motion, and apparatus therefore.
2. Description of the Related Art
According to Standard H.264 specifying encoding and decoding processes on a moving picture, the encoding and decoding processes are performed in units of multiple macro-blocks in the moving picture or in units of sub-blocks which are obtained by partitioning a macro-block into two or four parts. The encoding and decoding processes are performed based on a motion estimation process. The motion estimation process is performed by referring to a past picture or both past and future pictures. A picture referred to for encoding or decoding a current picture is referred to as a “reference picture.”
According to Standard H.264, there is provided a multiple-reference scheme where the macro-blocks and/or the sub-blocks refer to different reference pictures. The reference pictures in the multiple-reference scheme are determined as follows. Firstly, reference pictures recently encoded are stored. The number of the reference pictures is in a range between 1 and 16. Next, a motion estimation process is performed based on all the stored reference pictures. Next, a reference picture giving the best result of the motion estimation process is determined to be a reference picture for a current picture. The multiple-reference scheme shows a higher compression rate and a better image quality than a conventional reference scheme using only one reference picture.
However, the multiple-reference scheme has some problems. Since multiple reference pictures are stored prior to encoding a current picture, a large capacity of a memory is required. In addition, since a reference picture for a current picture is determined by performing a motion estimation process on multiple reference pictures, calculation amount greatly increases. Moreover, it is difficult to encode and decode moving picture data in real time.